AN/SPN-46 Precision Approach Landing System (PALS)

Precision approach and landing systems include Textron Systems' SPN 46 (V)1 and (V)2 automatic landing systems for aircraft carriers and amphibious assault ships.
Textron's AN/SPN-46 precision approach landing systems are
installed on all US Navy aircraft carriers.
The AN/SPN-46 provides safe and reliable final approach and landing guidance for Marine Corps helicopters and AV-8B Harrier VSTOL attack aircraft during day/night operations and adverse weather conditions. The AN/SPN-46 is capable of controlling up to two aircraft simultaneously in a "leapfrog" pattern because of two dual-band radar antennas/transmitters. As each approaching aircraft being assisted by the system lands, another can be "acquired". The AN/SPN-46 provides for a manually controlled approach (MODE III landing) in which the AN/SPN-46 air traffic controller relays to the pilot continuous updates on his position and direction. The AN/SPN-46 employs low-probability-of-intercept (LPI) technology to decrease the probability of passive detection by hostile forces. The AN/SPN-46 employs an X-band coherent transmitter and receiver utilizing monopulse tracking and doppler processing on received signals for clutter rejection and rain attenuation at an operating range of 8 nmi.

Air traffic controllers use three methods to guide aircraft onto the deck of an aircraft carrier. The AN/SPN-46 radar, or Precision Approach Landing System (PALS), provides what is called a mode 1 approach. When engaged a PALS approach provides a hands-off landing for the pilot. Pilots don’t use it often, prefering not to hand off much of the aircraft's controls to a computer but it is important for controller to be able to take control when all other systems fail. Another type of approach used is a mode II approach. Using a crosshair display, or “needles”, pilots line up
their approaches and get confirmation of their readings from a CATCC computer. The third type of approach, mode III, involves a controller “talking down” a pilot, providing the pilot with precise instructions for a safe landing.